Crackling FireFox with high CPU and high RAM?

I have a self-made PC (not mine, but from a friend I now have no contact with) and the PC has been going very well for 4 years. However, a Kinstern started jerky about 1-2 months ago, especially when I watch YouTube. I have no other task open on the side, just YouTube. Then the audio starts to crackle, pull slowly and the video also begins to hang and jump to different places (as far as the audio is).

As soon as this problem occurs, other things that I have open meanwhile start to hang (e.g. My Minecraft figure gets stuck in the air and then slowly falls down or my mouse lies over the screen).

I have already noticed that during these stutters in the Task Manager the CPU at FireFox is at 25-30% and the RAM at FireFox is over 1,000 MB.

Unfortunately I can't do much with it, I only know what to do when a task does not want to end etc. In the Task Manager, however, I do not know what to do next. I'm not particularly trained in PC usage and I don't know which parts are installed in my PC.

Has anyone already had these problems or can they give me tips on how to fix them? I have already looked up in several forums with people who had the same problem, but there was a lot of jargon. But I now assume that something in my PC may give up the ghost. However, I'm unsure because I don't even know what I have.

That will help you further https://support.mozilla.org/...lemloesung